1. Field of the Invention
The present invention relates to wiring substrates preferably used in high-density surface mounting of semiconductor devices and electronic apparatuses.
2. Description of the Related Art
Concomitant with higher density, higher speed, and increase in number of pins of semiconductor devices, surface-mounting boards have been required to have higher mounting density and finer wiring for mounting semiconductor devices or electronic apparatuses. Instead of conventional multilayer printed circuit boards, a multilayer printed circuit board has been formed by a multilayer buildup method and has drawn attention in response to the requirements mentioned above. The conventional multilayer printed circuit boards are formed by laminating prepregs of glass-cloth reinforced resin substrates provided with copper wirings, which is formed by etching beforehand, and then by drilling the laminated prepregs for providing a through hole therein so that wirings formed at different prepregs are connected to each other.
The multilayer buildup circuit boards are formed by steps of forming an insulating layer composed of, for example, an epoxy resin on a printed circuit board which is a core part, forming via holes in the insulating layer by exposing, developing, lasering, and the like, and forming a wiring on the insulating layer by a combination of sputtering, electrolytic plating, electroless plating, and the like. Since the multilayer buildup printed circuit board has no dead space formed by through holes, fine via holes can be formed, and as a result, a mounting substrate can be realized which has a higher mounting density.
In addition, recently, in order to simplify a method for producing the multilayer buildup printed circuit boards so as to reduce production costs therefor, methods has been proposed as disclosed in Japanese Unexamined Patent Publication (JP-A) No. H8-111584 (hereinafter referred to as conventional technique 1), in which copper-clad resin sheets are laminated, and then an insulating step and an electrical connecting step are simultaneously performed.
In particular, in the conventional technique 1, a laminate composed of a plurality of layers, that is, a copper foil, a polyimide sheet, and an adhesive sheet laminated from the top, is adhered on a substrate composed of a glass-cloth reinforced resin having a wiring on the upper surface thereof. Next, the copper foil located at the top is etched to provide an opening for forming a via hole, and then the via hole is formed by etching the polyimide sheet and the adhesive sheet located under the copper foil to the wiring on the substrate. Subsequently, an electroless plating layer is formed on the entire surface of the laminate so as to form an electric connection through the via hole, the copper foil provided at the top and the electroless plating layer are etched into a predetermined pattern so as to form a three dimensional wiring, and as a result, the multilayer buildup printed circuit board is obtained.
Compared to a general production process in which insulating and electrical connecting are sequentially performed, the conventional multilayer buildup printed circuit board has an advantage of simplifying a production process due to simultaneous operations of insulating and electrical connecting.
However, for forming a three dimensional wiring structure, since a subtraction method can only be used which is used for the wiring formation for general printed circuit boards, a fine wiring having a pitch of less than 100 xcexcm is not preferably formed by the conventional multilayer buildup method for the multilayer printed circuit board.
Meanwhile, in the conventional technique 1, wiring may be formed by an additive method which is capable of forming a fine wiring following a step of removing the entire copper foil after the formation of via holes.
However, in the method mentioned above, a step of removing the copper foil is additionally required, so that the advantage of simplifying the process is lost, and in addition, there is a problem in that electric connection reliability through the via holes is degraded since the wiring on the substrate is also etched out.
Accordingly, when an additive method is used, the production process becomes complicated and no advantages can be expected.
It is an object of the present invention to provide a resin laminated wiring sheet which is capable of forming a fine wiring by using a sheet lamination method effective to simplify a production process, and which is capable of forming multilayer buildup printed circuit boards and mounting boards having superior reliability.
It is another object of the present invention to provide a method for producing the resin laminated wiring sheet.
The problems described above can be solved by a wiring structure produced by a following process. Firstly, a resin laminated wiring sheet is prepared by coating an epoxy-acrylate photosensitive resin composition on a copper foil, etching the epoxy-acrylate photosensitive resin composition on the copper foil into a predetermined pattern by exposing and developing, and forming a conductive pattern composed of a metal deposited by plating at which the photosensitive resin layer is etched. Then, the wiring structure is formed by adhering the resin laminated wiring sheet onto a supporting substrate and etching the copper foil into a predetermined shape.
That is, in accordance with one aspect of the present invention, there is provided a resin laminated wiring sheet which is produced by coating an epoxy-acrylate photosensitive resin composition on a copper foil, etching the epoxy-acrylate photosensitive resin composition on the copper foil into a predetermined pattern by exposing and developing, and forming a conductive pattern composed of a metal deposited by plating at which the photosensitive resin layer is etched.
In accordance with another aspect of the present invention, there is provided a wiring structure formed by coating an epoxy-acrylate photosensitive resin composition on a copper foil, etching the epoxy-acrylate photosensitive resin composition on the copper foil into a predetermined pattern by exposing and developing, forming a conductive pattern composed of a metal deposited by plating at which the photosensitive resin layer is etched, and adhering a conductive pattern of a resin laminated wiring sheet onto a supporting substrate.
In accordance with still another aspect of the present invention, there is provided a method of producing a resin laminated wiring sheet, which comprises the steps of coating an epoxy-acrylate photosensitive resin composition on a copper foil, etching the epoxy-acrylate photosensitive resin composition on the copper foil into a predetermined pattern by exposing and developing, and forming a conductive pattern composed of a metal deposited by plating at which the photosensitive resin layer is etched.
In accordance with yet another aspect of the present invention, there is provided a method of producing a wiring structure which comprises the steps of coating an epoxy-acrylate photosensitive resin composition on a copper foil, etching the epoxy-acrylate photosensitive resin composition on the copper foil into a predetermined shape by exposing and developing, forming a conductive pattern composed of a metal deposited by plating at which the photosensitive resin layer is etched, adhering a conductive pattern of the resin laminated wiring sheet onto a supporting substrate, and etching a copper foil of the resin laminated wiring sheet into a predetermined shape so as to form the wiring structure.
As the epoxy-acrylate photosensitive resin composition which can be used for the present invention, an epoxy-acrylate photosensitive resin composition having a fluorene structure is preferably composed of a general formula (I) represented by chemical formula 1 shown below and on e of a polymerization initiator and a sensitizer. 
(n is an integer from 0 to 20, R1 is a carboxylic anhydride, R2 is a hydrogen atom or a lower alkyl group)
Since the epoxy-acrylate photosensitive resin composition has superior resolution compared to various conventional resins, such as a polyimide resin and an epoxy resin, and can be patterned by exposing and developing, the resin laminated wiring sheet provided with a high aspect ratio and a fine wiring pattern can be formed by a simple process using the epoxy-acrylate photosensitive resin composition. In addition, since the epoxy-acrylate photosensitive resin composition having a fluorene structure has not been treated at 100xc2x0 C. or more, and hence, is in a semi-cured state, the resin laminated wiring sheet can be heat-bonded to any supporting substrates, and the wiring structure provided with a high aspect ratio and fine wiring can be formed by a simple process. Furthermore, when necessary, a multilayer wiring structure can be formed by laminating the resin laminated wiring sheet provided with via holes or bumps.
In Japanese Unexamined Patent Publication (JP-A) No. 10-247772, superior resolution of an epoxy-acrylate photosensitive resin composition having a fluorene structure and a method for forming a conductive wiring pattern using the superior resolution of the epoxy-acrylate photosensitive resin composition mentioned above are disclosed.
However, in the method for forming the conductive wiring pattern and in the step of forming multilayer wiring, an epoxy-acrylate photosensitive resin composition having a fluorene structure are always used in a cured state. The reason for this is that the epoxy-acrylate photosensitive resin composition having a fluorene structure must have heat resistance and chemical resistance which are required by operation conditions, and a wiring structure cannot be formed when the photosensitive resin is in an uncured state.
In contrast, the resin laminated wiring sheet of the present invention can form a conductive wiring pattern by a simple process comprising a step of patterning the epoxy-acrylate photosensitive resin composition having a fluorene structure on the copper foil by exposing and developing, and a step of depositing a metal by electrolytic plating. Consequently, the epoxy-acrylate photosensitive resin composition having a fluorene structure is not necessarily cured, and hence, the wiring structure can be formed by a simple process of heat-bonding the resin laminated wiring sheet onto the supporting substrate.
In addition, the fact that the epoxy-acrylate photosensitive resin composition having a fluorene structure without being treated at 100xc2x0 C. or more can be heat-bonded to any supporting substrate was first discovered by the inventors through the intensive research and investigation to achieve the present invention, and the above fact cannot be derived from any papers published before.